It has been the practice in drilling deviated bore holes to employ bent subs and bent housings in connection with running strings, for example, drill strings employed in drilling oil wells.
The bent subs or the bent housings (see, for example, U.S. Pat. No. 3,260,318) introduce an angle into the drill assembly. The angle is related to the vertical angle of the desired deviation.
However, the bend angle practically permissible in the prior art for a single deviating unit is very limited, in the range of 1 to 3.degree., in order to that the drill string, in deep holes, may pass freely into the bore hole. In order to obtain a drilling assembly with a greater degree of bend, a combination of bent sub and bent housing may be used. If a greater bend than the one obtained by using a bent sub/bent housing combination is desirable, deviating units which may be bent after they are inserted in the hole, such as described in U.S. Pat. No. 3,627,356, may be employed.
Except accidentally, the plane of maximum bend angle direction of the axes of the angle deviating units with any arbitrarily selected plane through the axis of the drill string will vary in a random fashion as the string is made up.